Grenade launchers fire all kinds of grenades. Some are chemical, dispensing tear gas or nausea gas. Others eject flares for signaling, marking rounds with smoke, phosphorus for lighting fires, and regular high explosive grenades for anti-personnel purposes.
In combat situations, needs vary and there may be a need to hand-insert a special round in a multishot grenade launcher. To do this the feed mechanism must be inactivated, the chambered round removed, and the special round inserted. Also, in refilling the magazine, the feed mechanism feeds a second cartridge into chambering position behind the barrel when a round is already chambered. Since the barrel already contains a chambered round, the second cartridge in chambering position prevents the barrel from moving backward to the ready position, creating a malfunction. Also, if the cartridge case of a spent round fails to eject and stays in the barrel, it must be manually removed before a new cartridge can be chambered.